Diuretics are products that help to eliminate fluid from the body. They cause a loss of water by partially paralyzing water reabsorption, i.e. the rate of urination is elevated. Powerful diuretics can increase the flow of urine to about 6 liters per day.

Diuretics include substances such as:

• acetazolamide, amiloride, bumetanide, canrenone, chlorthalidone, etacrynic acid, furosemide, indapamide, metolazone, spironolactone, triamterene and thiazides such as bendroflumethiazide, chlorothiazide, hydrochlorothiazide
• and other substances with a similar chemical structure or similar biological effects.
  
  

They are prohibited in and out of competition except for drosperinone which is legal. Diuretics and other masking agents are the fifth in frequency of use drug class by 6.7% of all adverse analytical findings worldwide. The most frequently used substances are furosemide and hydrochlorothiazide by about 30% of all diuretic occurrences.

Masking agents are compounds that are taken with the purpose of hiding or "masking" the presence of specific illegal drugs that are screened for doping testing. Masking agents have the potential to impair or conceal the banned substance in the urine. Diuretics can be regarded as "masking" agents due to the dilution of the urine, which results in lower levels of the banned substance being excreted from the body.